import java.util.Scanner;

public class J1506 {
    public static int sum(int n){
        if(n == 1){
            return 1;
        }else{
            return n + sum(n - 1);
        }
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        System.out.println(sum(n));
    }
}
